Shielded electrical conductor construction and method of making the same



June 1s, 1946.

MCCUTCHAN SHIELDED ELECTRICAL CONDUCTOR CONSTRUCTION AND METHOD OFMAKING THE SAME Filed Feb. 24, 1945 lNvENTor-e1 6501665 L. /fc Can/AN.

\\m\.m.m

Patented June 18,- 1945 smspnsn Emoment. connuo'ron oon- STBUCTION ANDMETHOD 0F MAKING THE SAME Geol-ge L. Mscutehsn, Rosie. N. Y., asignar,to Rome Cable Corporation, Rome. N. Y., a corpo` ration of New YorkApplication February 14, 1945, Serial No. 579.623

i This invention relates to radio-shielded electrical conductor andterminal or connector con-n prooi' and insulating junctions may becifectively and dependably achieved between the radioshielded conductorconstruction and a point of mechanical and electrical connection such asa spark plug well, manifold or conduit connecting element, and the like.Another object .is to prdvide a construction of the above-mentionedcharacter in which insulating materials of different physical propertiesmay be employed for the terminal insulator and for the insulatingcompound filling the space between the conductor and the 5 Claims. (Cl.174-13) and relation and order oi' each of the same to one or more ofthe others. all as will be illustratively described herein. and thescope of the application of which will be indicated in the followingclaims.

In the accompanying drawing, in which is shown. by way of illustration,a preferred embodiment ofthe mechanical features oi my invention, l

Fig. 1 is a central longitudinal sectional view, certain parts beingshown in elevation and being partly broken away, of a radio-shieldedconductor structure in one stage of its construction according to mymethod;

Fig. 2 is an elevation. partly in longitudinal cross-section. showingthe construction in a succeeding stage:

Fig. 3 is a transverse sectional view along the line 3-3 of Fig. 2; and

Fig. 4 is a central longitudinal sectional view.

. parts throughout the several views of the drawshielding conduitwithout having the purposes and functioning of the one detrimentally af-`iected by the other. Another object is to provide va shielded conductorconstruction in which the terminal insulator is of a consistency orhardness to coact appropriately in eecting a sealed or gasketedmechanical connection. while the insulating or filler compound in theshielding conduit is of soft consistency, without having thecharacteristics or purposes of the one impaired by the other. Anotherobject is to provide a simple. practical, and emcient method for makingradio-shielded conductors with terminal insulators and capable of beingemciently carried on in practice with good uniformity of results.Another object is tc provide a practical method for dependablyasscmbiing and sealing the radio-shieldedconductoi' with filler'compound and a terminal insulator having' certain physical propertiesand functions different from those of the filler-all without iining.

Referring. first, to Fig.' 1, I preferably employl a conduit, generallyindicated by the reference character Il, which, for purposes ofeffecting radio-shielding, is metallic and preferably comu prises aflexible tube lll' made of helicallywound,

corrugated, strip sheet-metal, such as is shown in United States PatentNo. 1,198,392, employing.

' III" of braided metal strands, as shown and depairment of theproperties of the one by the propscribed in United States Patent No.1,340,818,l

snugly envelops the ilexible tubing In, being, of course, flexibletherewith, The ends of the conduit I0 are received 'in suitablecounter-bores Il* of a suitably shouldered ferrule I I. to which theyare secured in any suitable way to effect a sealed connection, forexample, as by soldering. The ferrules Il have shoulders or flanges Il.with which engage the end shoulders IP of nuts l2, internally threadedas at Ill. whereby the respective ends of the conduit It and relatedparts, later described, lmay be secured, for example, to theexternall'ythreaded shielding barrel or well I3 of a spark plug and. to.a similarly externallythreaded cylinder, or well. 'or socket Ilassociated with the manifold (not shown) in which the various spark plugconductors are contained. BY

means of the nuts I2, a mechanically secure connection to the parts I3and I4 may be made, and, moreover, in coaction with other parts laterdescribed, dependable sealed junctions can be eiIected-a-ll whileachieving, also, a desirable quick detachability of the lead andterminal structural unit.

Extending within the conduit III, and suitably insulated therefrom, is aconductor IB, which is preferably flexible and, hence, may be a strandedconductor; by way o! the conductor I6, the high potential energyrequired to energize the spark plug is to beconveyed, and to insulatethe conductor I6 from the radio-shielding metal parts of the conduit IIII prefer to employ an insulating covering I1 about the wire I5, and thisinsulation I1 may be of anydesired or suitable construction orcomposition, or of combinations of insulating compositions or elements,preferably adequate to dependably insulate the wire I8 for the voltageof the energy it is to carry, with usual or appropriate margins ofsafety. The wire I6 extends preferably coaxially of the conduit I0,which contains a suitable insulating compound I8 which can, if desired,be of a dielectric strength such as to provide for the adequateinsulation of the wire I6 from the conduit I0 independently of theinsulating covering or' sheath I1 which, in such case, need not beemployed, if desired, in so far as certain features of my invention areconcerned. 'I'he compound IB may be of any desired composition ormaterial, preferably relatively ilexible, and where the insulation I1about the wire I6 is omitted, the consistency of compound Il ispreferably such as to coact in maintaining the conductor substantiallycoaxially within the conduit III. or any other known means may beemployed to maintain substantial coaxial relation.

With the insulating sleeve I1 about the wire Il, however, manyadvantages are achieved; for example, precise coaxial relation need notbe provided for; the compound Il can, desirably, be of more advantageousconslstencies, preferably relatively soit or ilowable, and thus betterachieve, particularly when under compression, a more eilicient and morereliable filling of all of the space within the conduit I and about theinsulated conductor II1, and thus better guard against corona eil'ectsand against possible dielectric breakdown.

Any suitable means may be employed to inject the insulating compound I8into the space between the conductor and the internal walls of theconduit, as by injecting a suitable quantity thereof upon completion ofthe assemblage of the ferrules and nuts to the conduit III, and, bymeans of the nuts, suitable connection may be made to any suitableapparatus for injecting the material Il.

Having injected a suitable quantity of the compound Il into the spacebetween the conductor and the conduit walls, the compound Il being insuitable plastic condition and being, illustratively, made up of anysuitable uncured rubber-like material, such as natural rubber, any ofthe synthetic rubbers, or the like, each suitably componded, such of thecompound Il as projects beyond the outer ends of the ferrules II isremoved or cleaned off, so `as to leave the end boundary of the materialIB substantially along a plane indicated at I9-all substantially asindicated in Fig. i-the filler compound III being preferably compounded,in known manner, as by adding suitable ingredients or fillers thereto,so that,

upon the application of heat to cure it, it swells or expands insubstantial or appropriate extent and so that, upon completion of thecure, it is preferably not hard or rigid, but has sufcient softness tobe adequately flexible so as to bend with the bending of the conduitII), as may be necessary.

Since the steps 0f my method and structural features according to myinvention may be employed to construct the insulating terminal at eachend of the conduit I0, it will suiiice to describe in detail the stepsand apparatus, and the parts employed, with respect to one end cf theconduit l0. The conductor I6, as shown in Fig.

1, projects beyond the end of the conduit It throughout a lengthcommensurate with the length of the insulated terminal structure to beemployed, and, where the conductor I5 vhas an insulating jacket I1thereabout, the jacket I1 is stripped from the extreme end portion cithe conductor I6, thus to bare enough of the wire Ii to permit theapplication and connection thereto ci any desired form of contact orterminal.

Onto the projecting end of the conductor I now sleeve an axially shortbushing 2D of insulating material having a bore 2li of a diameter suchthat the conductor structure IS--Il passes therethrough relativelyeasily, and the ilt therebetween may be not too snug, and having anoutside diameter such that the cylindrical face 2l is readily receivedwithin the conduit I0. The bushing 20 is preferably of a length,relative to the ierrule II, substantially as indicated in Fig. 1,V andis slid along the conductor structure I8--I1 and into the conduit III sothat its inner face abuts against the filler compound Il along theabove-mentioned plane I 9, leaving the front or outer end face of thebushing 2l preferably spaced inwardly somewhat relative to the mouth ofthe ferrule II.

The bushing 2l is made of asuitable insulating compound such as any ofthose earlier above mentioned, but compounded so that it is cured orvulcanized, prior to insertion or assembly, as above described, in anysuitable mold or the like, to substantial hardness, though stillretaining, if desired, some degree of resiliency; thus it may bepremolded of natural rubber, lsynthetic rubber, or the like,appropriately compounded, and molded and cured or heat-treated in anysuitable way. In such form it is easily assembled to the parts, asindicated in Fig. l, requiring simply that it be sleeved onto theconductor and slid into the end of the conduit. v

To the projecting portion of the conductonis now applied a. suitableinsulating material, shaped to form a suitable insulating sleeve orterminal insulator, and preferably the material, in the form of uncuredor unvulcanized compound of .natural rubber, synthetic rubber, orthelike,

preferably compounded to cure or vulcanize to suitable toughness andhardness, with some resiliency, is applied in the form of tape-likeelements which are wrapped about the projecting portion of theconductor, the wrapping being applied in such varying numbers of layersas to approximate or generally simulate the ultimate shape orconfiguration which it is desired that the terminal insulator is tohave. In Fig. 2 the insulating material or compound so applied isindicated by the reference character 2I, and in its initial applicationit is made to extend up against the end face of the precured annulus orinsert 20, and also to iill in the angularities at the outer ends of theferrules II, as well as to simulate in of the mold cavity and ol?l the'errule Il.

amato-i even when cured, contamination of the compound 2l, particularlythose portions of it that form the shoulder 2|, by'commingling therewithor flowing thereover of the compound i8, is avoided according to certainfeatures ol' my invention.

Themass of insulating compound 2|, at each t end of the structure, isnow ready to vbe conformed to its final, nnished shape or connguration,and for this purpose I preferably employ a sectional mold M,conveniently made up of two blocks Ml and M2 of metal, each providedwith a mold cavity 28, the two mold cavities 2l being complemental toeach other, and, when assembled and brought in face-to-face contact, asshown in y Fig. 2. the complemental mold cavities 2l, 2l, preferablycircular in cross-section, provide a conguration of the shape anddimensions which it is desired to give the insulating material 2|. Themold` sections M1, M2 may be provided Awith suitable ldowels and dowelcavities, indicated at 28, to guide and align them for assembly one tothe other, and are preferably also provided with arcuate recesses 30,each of `180 degrees extent, shaped to snugly envelop and encaseportions of the outwardly-projecting radial ilange or shoulder Il of theferrules H, so that the mold sections M1 and M2 can envelop the nange orshoulder Ilb and thereby become dependably se'- cured to the conduit andI feri'ulo assembly, the nuts I2 being at each end sleeved away from theferrules so as not to interfere with the ap- .plication of the moldsections.

The sectiona1 mold M has an end closing wall .3|, half of which is inone mold section and the other half in the other mold section, and thewall 3| or the mold cavities 28-28 may, if desired, be given anysuitable configuration to accommodate any desired form of conductiveterminal contact, indicated at 32 in Fig. 2, and which may be applied inany suitable way to the bared end of the wire I6 at any suitable pointin the process, illustratively, just before the compound 2| is wrappedin place, as above described.

The material v2| is 'applied in an amount somewhat in excess of thevolume which the mold cavity 28-28 has when the two mold sections arebrought tightly together, and, hence; when the sections of the mold areapplied externallythereto, it requires the application of adequate forceor pressure to bring the mold sections M1, M2 together and to bringtheir mating faces n and 39 into substantial contact, with the resultthat the moldable or plastic compound 2| is subjected to increasingcompression as the escape orifice between the approaching mold faces and39 .is diminished and nally closed.

The resultant pressure compacts the compound 2| tightly against andabout the conductor structure which it env'elps. and also causes someiiow or movement of the compound 2| in a direction inwardly against theprecured insert 2l, being also compactly conformedl to theconfigurations The material 2| is, thus, also compacted tightly againstthe insert 20, which in turn is compressed inwardly against the compoundI8', taking up any possible play or looseness'which might have occurredwhen the insert 2l was initially set into place. The insert 20, beingappropriately cured and, thus, having adequate rigidity for the purpose,may also serve to hold the conductor structure substantially coaxiallyof the conduit lll and ferrule ll, and thus prevent radial displacementthereof should, thereby, for' any reason, a radially-acting differentialforce tend to radially displace the conductor as the two mold sectionsare forced into closing position.

The effect of the closing of the mold sections.

M1, M2 in putting the compound 2| under substantia1 pressure, so thathydraulic ilow thereof takes place axially inwardly against the insert20, has the advantage that, according to the selected looseness of litbetween the bushing insert 20 and the conductor structure and theinternal wall of the conduit I0, some of thecompound 2| is forcedinwardly into the narrow annular crevices or spaces between these parts,and it may or may not, according to circumstances, reach the compound I8which, under the pistonlike action of the insert 20, becomes subjectedto some pressure to oppose this action, and probably some of thecompound, which is preferably compounded to be more lowable than thecompound 2|, enters these annular crevices from the other side of theinsert 20. Thus some compacting of the ller material I8 against both theconductor and the walls of the conduit may be effected at this stage,since the material I8 can thus be subjected to some pressure.

During this action at one end'o the spark plug lead, any suitable meansmay be employed at the other end to prevent the exerted axial pressureupon the illler i8 from causing it to emerge from the other end of theconduit, and aconvenient means for this purpose, as is indicated in thedrawing, mayV comprise a companion insert 20 and a companion sectionalmold M with insulating compound 2|, all applied at the other end of thespark plug lead, so that the processing steps may be carried onsubstantially simultaneously at both ends.

Any suitable means (not shown) may be employed to force the moldsections together to exert the above-described hydraulic forces and tohold them securely assembled upon having brought their mating faces "-38together; such a means may be a screw clamp or the like which, inholding the mold sections together, holds them also securelyinterengaged with and locked to the ferrule Il. With both ends of thelead structure thus provided with assembled and clamped molds, asindicated in Fig. 2, the entire entity may now be subjected to suitableheat treatment toI eiect curing of the compound I8 within the conduit Iland of the compound 2| at-each of the terminal ends, these compounds andalso the material of the cured inserts being so selected and being socompounded that, during curing,

they become integrally joined or united with each other throughout suchareas where they are brought into contact with each other, as abovedescribed, thus forming a continuous and uninterrupted insulatingenvelope about the conducdescribed pressures and those later hereinmentioned insuring that these unions take place dependably so that apossible leakage path, extending radially, does not result, so thatdielectric strength is not impaired, as by included layers l7 of air orgas, as might be the case ii such junctions were not 'eifectedPreferably the materials employed for the illler I8, and also for thesleeve or terminal insulating material 2|, are compounded, in knownmanner, to include ingredients so that, upon the application of heat forcuring or vulcanization, some swelling of the compounds takes place,particularly of the compound il, thus increasing such pressures as theymay already be subjected to as a result of the above-described closingof the mold sections.

The increased pressure to which the compound il is thus subjected, andthis is desirable in order that the compound il be tightly compactedagainst the conductor structure and against the conduit walls, has theeffect of causing some flow of the compound Il, at its respective ends,in directions outwardly of the conduit I0, and, were any of itallowed'to creep or ow, during curing, along the surfaces of the ferruleIl and thus reach the shoulder 2l, it could commingle with the compoundof the shoulder 2|* or overlie the external surfaces thereof by movementalong thc faces of the mold cavity 2I2I. Detrimental contamination ofthe shoulder 2|* would thus result, for the compound 2| is compounded tocure to substantial hardness with suillcient resiliency so that theannular shoulder 2|* can, in

the ultimate installation of the spark plug lead,`

be mechanically clamped and form a dependable seal, while the compoundI8 is compounded to cure to relative softness, and, hence, isinappropriate for gasketing action. Such contamination of thegasket-forming shoulder 2|l has been found, according to certain priorattempts, to take place mainly in certain portions only of theperipheral extent of the shoulder` 2|", giving rise to so-called softspots" through which the gasket gives way.

According to my process, however, the insert 2l, at each end, takes partin guarding against such contamination. The annular spaces between itand the conductor and the conduit wall provide axially long paths ofpossible movementI of the filler compound Il and, thus, coaet to isolatethe gasket shoulder 2 I* from the contamilnating material; these pathsof flow, moreover,

are substantially sealed at their outer ends by the entry thereinto ofcompound 2| under pressure as a result of the clamping together of themold sections and, in efi'ect, seal off these possible narrow passages,thus blocking material flow of the filler Il, these actions being aidedby the comparative narrowness of the annular spaces or crevices withinwhich the correspondingly radially thin layer of compound 2| is dimcultor impossible to displace by the more liquid or more owable llercompound Il. In thus preventing detrimental escape of filler compound Ilfrom the conduit I0, during cure, a better compacting of the filler Ilwithin the conduit i and about the conductor is effected, because itsexpansion or swelling during cure is substantially unaffected by escapeof material portions of it. Thus, also, the expansion of the fillercompound il during cure can act hydraulically against the insert 2li,causing the latter, in turn, to exert pressure upon the compound 2| thatis under- Boing cure also, and, in exerting such piston-like pressurethereon at the inner end thereof, presses the compound 2| against theferrule surfaces and also more tightly into the. mold cavity,particularly the shoulder-forming cavity portion, and thereby alsolessens accessibility of filler com- 8 pound I8 to the shoulder portion2P. This piston-like action can also function to more tightly compactsuch of the compound 2| as has entered, or is additionally made toenter, the annular crevices at the outer and inner annular faces of theinsert 20.

Upon completion of the cure, the mold' sections are removed and thecompleted structure is ready for installation in the vmanner abovedescribed and as is indicated in Fig. 4, where the nuts I2 are shownthreaded onto the casing or well parts |2|4 to compress the gasketflanges 2|* securely in sealing relation between the ferrules and theparts il and I4, respectively. In such sealing relation and action, itis only the cured material of the terminal insulators 2|, specificallyappointed, as above mentioned, for gasketing action, that eifects thedesired sealed relationships; the sealing flange in each case has auniform sealing action, being unaifected or uncontaminated by the soft,cured filler II, the characteristics of which are appropriate forcoaction between the conduit and conductor and other parts, but are notappropriate to take part in a gasketing or sealing action. Were thesealing flange to be contaminated, in whole or in part, 4as by leakageabove mentioned, dependability or permanency of seal would not beachieved and, instead. rapid failure would result at the point or pointsof contamination, it being understood that the sealed connectionsometimes has to withstand substantial pressures. such, for example, ascould be caused by leakage of high-pressure gases from the enginecylinder through the spark plug connection thereto.

In Fig. 4 the'parts 2|, 20, and Il are crosshatched as they appear inFig. 2, which illus* trates one stage of the process, but in Fig. 4 theadjacent lines of demarcation between these three Iparts are indicatedin broken lines to indicate the integral uniting together of the threeparts at the respective faces of the inserts 2|).

As above indicated, the filler Il and the material of the terminalinsulator 2| may be compounded out of any suitable insulating materialsand ingredients, all for the purposes above described. Illustratively,and preferably, neoprene is employed for both, the compounding thereofbeing suitably or appropriately varied according to the respectivecharacteristics desired for the nller Il and terminal insulators 2|.Whatever materials are employed, such as those earlier above mentioned.the respective com- .pounding thereof for the nller il and for theterminal insulators 2| may be effected, in any known manner, to give thefiller Il, when cured. A Shore durometer reading on the order of'15 anda Shore durometer reading for the material of the insulators 2|, whencured, on the order of 85. Where substantial swelling of the illler Ilduring cure is desired. suitable ingredients are added in thecompounding thereof to cause materially greater swelling thereof duringheat treatment than it might normally have, and also some control of thefactor of swell may be effected by correspondingly controlling theextent and character oi' mechanical working of the compound, as on milirolls. Additions, during mechanical working, of oils, such as an oil ofpetroleum base, or of other suitable oleaginous substances which becomewell and highly dispersed throughout the material, may also be employedto materially increase the swelling characteristics, and, when employed,they have the additional advantage of plasticizing the compound andacting as a lubricant, to facilitate injection of the illler I8 into thespace between the conductor and the internal walls of the conduit; insuch case the rubber-like base material employed is preferably selectedfrom the types that are oil-resistant, of lwhich neoprene is a goodillustration. that other llers and ingredients usually employed inotherwise plasticizing and processing rubber or rubber-like materials,and including plasticizing agents, vulcanizing agents, accelerators,retardants, or the like, may and preferably are also employed inrespective amounts or proportions to give the desired processing andcuring characteristics. The material yof t the member 20 may be, andpreferably is, compounded and cured to have characteristics simiiar tothose above described in connection with the material ce?. terminalinsulator 2|; as earlier above noted, member 20 is preferably molded andcured before its insertion into the assemblage,

It will thus be seen that there has been provided in this invention aradio-shielded cona ductor and terminal insulator construction andmethod of making the same in which the various objects above noted,together with manythoroughly practical advantages, are successfullyachieved. The construction is thoroughly dependable and of uniformaction, and it will be seen that the method can be reliably carried outin practice with the attainment of consistent results conducive toquantity production.

As many possible embodiments may be made of the mechanical features ofthe above invention and as the art herein described might be varied invarious parts, all without departing from the scope of the invention, itis to-be understood that all matter hereinabove set forth, or shown inthe accompanying drawing. is to be interpreted as illustrative and notin a limiting sense.

I claim: Y

, 1. In a method of preventing contamination of the gasket-formingportion of an external terminal insulator by the vulcanizable insulatingcompound within the conduit of a radio-shielded lead that has fittingsat an end thereof that comprise a ierrule that is in fluid-tightconnection with the conduit and that'has an annular face against whichto receive a gasket, the steps which comprise placing a conductor withinthe conduit with a portion projecting beyond said ferrule, illling theannular space -between the conduit and the conductor with a vulcanizableinsulating compound that is compounded'to expand upon heat treatment,inserting through the errule and into the end of the conduit an" annularmember of substantial length made of a cured insulating material bysleeving it onto the projecting end of said conductor and dimensoned tosubstantially close ofi mechanically said annular space at the end ofsaid insulating compound, thereby providing two restricted, annular,high-resistance paths of possible flow, one between the conductor andsaid member and the otherlbetween said member and the conduit wall,molding an insulating material about the projecting portion ci saidconductor and into engagement with the end face of said member and to:torni also an annular gasket-forming shoulder engaging said ferruleannular face and hoiding the molded insulating n material in place by adetachable enclosing mold.

And it will be understood and subjecting the assemblage to heattreatment to-cure said molded insulating material and join it to saidmember and to cure said insulating compound and join it to said vmemberand to expand it, said high-resistance paths of flow accommodating inpart surplusage of compound caused by its expansion and protecting saidannular gasliet-forming portion of said molded insulating materialagainst access thereto of and contamination by said compound.

face against which to receive a gasket, the steps which comprise placinga conductor within the conduit with a portion projecting beyond saidferrule, filling .the annular space between the conduit and theconductor with a vulcanizable insulating compound, inserting an annularmem ber made of a cured insulating materia1 and being of substantialaxial length into the end of the conduit and into engagement with thecompound in the conduit and thereby provide two restricted,high-resistance paths of possible flow, one between the conductor andthe member and the other .between the member and the conduit, assemblingto the ferrule and about the projecting portion of the conductor anuncured insulating material shaped in the form of a terminal insulatorand provided with an annular, gasket-forming portion engaging saidannular ferrule face, and subjecting the assembled entity to heattreatment and pressure to 'cure the material of the terminal insulatorand join it integrally to said cured member and to cure said compoundand join it integrally to said cured membelri, said restrictedhigh-resistance paths accommodating, in part at least, fiowable compoundand protecting said annular gasket-forming portion of the terminalinsulator from access thereto of and contamination by saidcompound.

3. In a method of preventing contamination of the gasket-forming portionof an external' terminal insulator by the curable insulating compoundWithin the conduit of a radioshielded lead that has means at an endthereof providing an annular face against which to receive a gasket, thesteps which comprise placing a conductor Within the conduit with aportion projecting from 'said end, closing ofi the annular space betweenthe conductor and the conduit adjacent said end by inserting therein anannular member of relatively rigid insulating material and therebyprovide two restricted, high-resistance paths of possible fiow, onebetween said member and the conductor and the other between said memberand ible, non-rigid condition within the space between the conductor andsaid conduit and against said member, and curing the assemblage underconditions of pressure applied to said compound within the conduit tocause it to be compacted against the/conductor and against the conduitwalls whereby, during cure, said high-resistance paths oppose materialilow thereinto of com pound under pressure and thereby protect saidannular portion that engages said annular face against access thereto ofand contamination by said compound.

4. A radio-shielded lead with terminal gasket forming insulatorcomprising a :luid-tight radioshielding conduit having a Ierrule influid-tight connection therewith at an end thereof, said ferrule havingan annular gasket face for the reception thereagainst ot a gasket, asleeve-like terminal insulator of cured relatively rigid insulatingmaterial extending from said Ierrule and having an annular gasketportion to overlie said annular i'errule face. a conductor extendingwithin said conduit and through said sleeve-like terminal insulator, acured relatively ilexible insulating compound within said conduit andabout the conductor thereinl there being interposed between the ferruleend of said terminal insulator and said cured compound an annular membero! relatively rigid insulating material that is integrally united withthe material o! the terminal insulator and with said cured compoundunder conditions of pressure of said compound during cure and ofrelationship of the annular surfaces o! said interposed member to thewall of the conduit and to said conductor as to provide restrictedhigh-resistance paths of possible ow of compound under pressure duringcure to thereby protect the annular gasket portion oi' said terminalinsulator against access thereto oi and contamination by said compound.

5. In a method of preventing contamination of the gasket-forming portiono! an external ter- 12 minal insulator by the curable insulatingcompound within the conduit of a radio-shielded lead that has means atan end thereof providing an annular face against which to receive agasket, the steps which comprise placing a conductor within the conduitwith a portion projecting from said end, closing of! the annular spacebetween the conductor and the conduit adjacent said, end by insertingtherein an annular member of relatively rigid insulating material andthereby provide two restricted high-resistance paths o! possible ilow,`one between said member and the conductor and the other vbetween saidmember and said conduit, applying about the proiecting portion of saidconductor a member of insulating material shaped in the form ot aterminal insulator and having an annular portion engaging said annularface, applying an insulating comby said compound.

GEORE L. MCCUTCHAN.

